Do they expire? Previousy IE VMs from Microsoft were only valid for ~90 days or something and required re-downloading (and then re-configuring all settings which was pita).
Follow @IEDevChat for updates and stuff.
http://blog.reybango.com/2013/02/04/making-internet-explorer...
take note of anything you upgraded since so you can create a new 90 day snapshot with more of the recent updates